Frequency of Carbapenem Resistance among Gram Negative Pathogens in a Tertiary Care Hospital in Southern Pakistan

Carbapenems are considered the treatment of choice for treating the multi-drug resistance Gram negative bacteria. But resistance to these antibiotics has increased worldwide thus limiting therapeutic options for clinicians. To investigate the frequency and Minimum Inhibitory Concentrations (MICs) of carbapenem resistance in Gram negative organisms at a tertiary care hospital in Southern Pakistan. Seven Hundred and ninety-three carbapenem resistant isolates were identified from different clinical microbiology specimens including blood, urine, pus, wound swabs, tracheal aspirate, catheter and CVP tip. All specimens were processed within 2 h of collection by standard microbiological technique. Antibiotic susceptibility testing was performed by the modified Kirby-Bauer disk diffusion method. Clinical Laboratory Standard Institute (CLSI) was used as reference guide for interpretation of results. MIC testing of imepenem and meropenem was performed on automated Phoenix TM 100. Carbapenem resistance was observed in Enterobacter cloacae (77%), Acinetobacter spp. (60%), Pseudomonas spp. (17.5%), Klebsiella spp. (6.1%), Proteus spp. (1.6%) and E. coli (1.4%) during the year 2010-2014. Trend of resistance observed was 3.2% (51/1150), 3.3% (70/2103), 5.7% (167/2917), 5.8% (172/2950) and 10.0% (333/3329) respectively indicating a rising trend during the study period. MIC testing of imipenem and meropenem was performed by Phoenix TM 100. In 2013, 97 carbapenem resistant isolates were tested for imipenem MIC of which 89 isolates showed MIC >8(µg/mL) while of the 58 isolates tested for meropenem MIC, 54 showed MIC >8(µg/mL) for meropenem. In 2014, 184carbapenem resistant isolates were tested for imipenem MIC and 176 for meropenem MIC of which 155 isolates has MIC >8(µg/mL) for imipenem and 144 isolates has MIC >8(µg/mL) for meropenem. The study shows annual increasing trend of carbepenam resistance in a tertiary care setting in Southern Pakistan thus indicating and identifying serious therapeutic and epidemiological risk of spread of carbapenem resistance. Majority of isolates showed MICs of >8(µg/mL) for both imipenem and meropenemin high frequency. Therefore, continuous monitoring via systemic surveillance studies are necessary to screen resistance in other settings of Pakistan.